Astrodendrum Döderlein, 1911

Okanishi, Masanori & Fujita, Toshihiko, 2018, A taxonomic review of the genus Astrodendrum (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) with description of a new species from Japan, Zootaxa 4392 (2), pp. 289-310 : 290-291

Genus Astrodendrum Döderlein, 1911

Astrodendrum Döderlein, 1911: 38 ;— Fell, 1960: 8. Baker, 1980: 16, 56. McKnight, 2000: 55.

Type species: Gorgonocephalus sagaminus Döderlein, 1902 .

Included species. A. capense ( Mortensen, 1933) ; A. elingamita Baker, 1974 ; A. galapagense A. H. Clark, 1916 ; A. laevigatum ( Koehler, 1897) ; A. sagaminum ( Döderlein, 1902) ; Astrodendrum spinulosum sp. nov.

Diagnosis emended. Arms five, branching. Number of arm segments less than six before first branch. No rows of calcareous plates on edge of disc margin. One madreporite situated on innermost portion of interradial lateral disc. Hooklets on aboral arms with one secondary tooth. Disc covered by variously shaped external ossicles or lacking any ossicles.

Remarks. Only external ossicles of the disc have been used as a taxonomic character for Astrodendrum in recent taxonomic papers ( Baker, 1974, 1980; McKnight, 2000). However, up to now, shape, size and arrangement of the external ossicles have not been sufficiently described for any Astrodendrum species other than A. elingamita .

In this paper, the re-examination of the type specimens of A. capense , A. galapagense and A. sagaminum revealed that these characters clearly distinguish these three species from A. elingamita . No type specimen of A. laevigatum was examined during this study due to missing information on its deposition. However, the original description of A. laevigatum mentioned that this species lacks any external ossicles on the disc.

During study of the type specimens of A. capense , A. galapagense and A. sagaminum together with a comparison of previous descriptions of A. elingamita and A. laevigatum , we found three new taxonomic characters to distinguish these three species: i) absence/presence of bulges on lateral ridges of proximal portion of the arm; ii) number of terminal projections of arm spines on proximal portion of the arm; and iii) number of secondary teeth of hook-shaped arm spines on distal portion of the arm (see also Remarks of Astrodendrum spinulosum sp. nov.; Table 1).

McKnight (2000) stated “the disc with granular external ossicles in various size” as a diagnostic character of the genus Astrodendrum . However, as mentioned above, A. laevigatum lacks any external ossicles and A. spinulosum sp. nov. has conical external ossicles on the disc ( Koehler, 1897, 1899; see also Remarks on Astrodendrum spinulosum sp. nov.). Therefore, we amended this diagnostic character to “the disc covered by various shaped external ossicles or none at all”.

External features of Astrodendrum laevigatum are distinctive in the genus, and this species should possibly be separated from the other congeners. However, we here refrain from establishing a new genus for this species because we have not observed any type specimens of A. laevigatum . To confirm exact taxonomic position of A. laevigatum , molecular phylogenetic study of Astrodendrum including A. laevigatum as well as observation of the type specimen are required.

This genus is widely distributed in the western Indo-Pacific to Atlantic Ocean, in a depth of 40–1314 m ( Fig. 1 ).

Figures

FIGURE 1. Distribution of Astrodendrum spinulosum sp. nov., A. capense, A. elingamita, A. galapagense, A. laevigatum and A. sagaminum. Red symbols indicate type localities.